1. Field of the Invention
The present invention relates to an electrical pickup for a stringed instrument having ferromagnetic strings, such as a guitar.
2. Prior Art
Single coil electrical pickups operating by means of magnetic induction such as those disclosed in U.S. Pat. Nos. 3,588,311 and 3,711,619 tend to couple with the stray magnetic fields produced by electrical devices such as motors, transformers and fluorescent lights. This coupling commonly produces an audible hum in the amplifier and speaker driven by the pickup. This hum commonly has a 60 Hz frequency, due to the use of 60 Hz alternating current power. Prior attempts at the reduction or elimination of this hum have been proposed which utilize two coils disposed side by side with parallel axes such as in U.S. Pat. Nos. 2,896,461, 3,902,394, 3,916,751 and 3,983,777, or with the two coils disposed one above the other, separated by a flat magnetic shield such as in U.S. Pat. No. 3,657,461. The first method causes string vibrations to be sensed over a relatively broad length of string, and results in cancellation of various frequencies, due to the spacing of the coils under the strings. The second method functions effectively as regards reproduction of frequencies generated by the instruments' strings, but has the disadvantage of not producing a strong signal. Additionally, pole legs extending around the strings in single coil pickups have been proposed to reduce hum in U.S. Pat. Nos. 3,236,930 and 4,026,178.